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Re: PMDD - Phosphate limited?

On Wed, 17 Nov 1999, David wrote:

> What does it mean to be phosphate limited or limited period?

There are always(?) factors in a plant's environment that restrict its
rate of growth.  Whatever is most restrictive is the limiting factor.
This could be the availability of any essential nutrient, light,
temperature, and so on.

"Availability" doesn't just mean "concentration in water".  Nutrients are
available from the water or from the substrate.  Water movement around the
plant alters nutrient availability as does the presence of some symbiotic
organisms and the chemical state of some nutrients.

If the availability of phosphate is most restrictive to plant growth, then
growth is said to be phosphate-limited.

I think the only way you can accurately determine which factor is limiting
is to vary each factor independently.  The limiting factor is the one that
when varied generates the greatest change in growth.  With an
understanding of the factors that influence plant growth it's usually
possible to narrow the list of possibly limiting factor down to a few
items and to determine their status with simple tests.

Once you know what is limiting you can decide whether you want to change
it and how you want to change it.  PMDD gives you one way to manipulate
nutrient - limited tanks.

Roger Miller